riscv: dts: thead: lichee-pi-4a: enable HDMI

riscv: dts: thead: lichee-pi-4a: enable HDMI

Lichee Pi 4A board features a HDMI Type-A connector connected to the
HDMI TX controller of TH1520 SoC.

Add a device tree node describing the connector, connect it to the HDMI
controller, and enable everything on this display pipeline.

Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
Tested-by: Han Gao <gaohan@iscas.ac.cn>
Tested-by: Michal Wilczynski <m.wilczynski@samsung.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Drew Fustini <fustini@kernel.org>
Signed-off-by: Drew Fustini <fustini@kernel.org>